This invention relates to a measuring device comprising at least two transducer units each provided with a sensor for sensing an input quantity and for producing a signal which is dependent on the input quantity, and also comprising a normalization circuit which determines the ratio of a linear combination of input quantities to the sum of the input quantities.
The invention also relates to a normalization circuit suitable for use in a measuring device in accordance with the invention.
A measuring device of this kind is known from the publication "Optical position sensing using silicon photodetectors" by Bill Light in Lasers and Applications, April 1986, pp. 75-79. The cited article describes some position-sensitive detectors (PSD) which are constructed using photodiodes in a bi-cell, quadrant and lateral configuration. Such detectors enable, for example determination of the position of a laser spot. The signals required for the X and Y displacement of the spot can be found by suitably summing or subtracting the diode currents, followed by normalization to the total intensity. To this end, the detectors described in the cited publication comprise two or four current-voltage converters for first converting the signals to the voltage domain, a number of subtraction and summing circuits, and two analog dividers. The drawbacks of those detectors are that the procedure is rather complex and that a variety of errors is introduced by the various components.